LC Chemistry Definitions

Dalton's Atomic Theory

1. All matter is made up of very small particles called atoms

2. All atoms are indivisible. They cannot be broken down into simpler particles

Properties of cathode rays

1. Travel in straight lines.

2. Cause glass to fluoresce.

3. Posses energy to turn paddle wheel.

Energy level

The fixed energy value that an electron in an atom may have.

Heisenberg uncertainty principle

It is impossible to measure at the same time both the velocity and position of an electron

Orbital

a region in space within which there is a high probability of finding an electron

Sublevel

A subdivision of a main energy level consisting of one or more atomic orbitals of the same energy

Element

A substance that cannot be split into simpler substances by chemical means

Triad (Doberiener)

A group of three elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two

Octave (Newlands)

Arrangments of elements in which the first and eighth element, counting from a particular element, have similar properties

Mendeleev's Periodic Law

When elements are arranged in order of increasing atomic weight the properties of the elements recur periodically

Modern Periodic Law

When elements are arranged in order of increasing atomic number, the properties of the elements recur periodically

Relative Atomic Mass

The average of the mass numbers of the isotopes of an element, as they occur naturally, taking abundances into account, relative to one twelfth the mass of a Carbon-12 atom

Principle of Mass Spectrometry

Charged particles moving in a magnetic field are deflected to different extents according to their masses and are thus separated according to these masses

Aufbau Principle

When building up the electron configuration of an atom in its ground state, the electrons occupy the lowest available energy levels

Hund's Rule of Maximum Multiplicity

When two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs

Pauli Exclusion Principle

No more than two electrons may occupy an orbital, and they must have opposite spin

Ionic Bond

The force of attraction between oppositely charged ions in a compound. Ionic bonds are always formed by the complete transfer of electrons from one atom to another

Transition metal

A metal that forms at least one ion with a partially filled d sublevel

Valency of an element

The number of atoms of hydrogen or any other monovalent element with which each atom of the element combines

A sigma bond is formed by...

the head-on overlap of two orbitals

A pi bond is formed by...

The sideways overlap of p orbitals

Electronegativity

The relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond

Van der Waals forces

Weak attractive forces between molecules resulting from the formation of temporary dipoles. They are the only forces of attraction between non-polar molecules

Dipole-dipole forces

Forces of attraction between the negative pole of one polar molecule and the positive pole of another polar molecule

Hydrogen bonds

Particular types of dipole-dipole forces between molecules in which hydrogen atoms are bonded to the small, electronegative elements nitrogen, oxygen or flourine. The hydrogen atom carries a partial positive charge and is thus attracted to the electronegative atom in another molecule. Thus, the hydrogen bond acts as a bridge between the two molecules.

Reagents to test for chloride anion

silver nitrate solution, dilute ammonia solution

Reagents to test for sulfate and sulfite anions

Barium chloride solution, dilute hydrochloric acid

Reagents to test for carbonate and hydrogencarbonate anions

dilute hydrochloric acid, magnesium sulfate solution

Reagents to test for nitrate anion

Iron(II) sulfate solution, concentrated sulfuric acid

Reagents to test for phosphate anion

Ammonium molybdate solution, concentrated nitric acid

Atomic radius

Half the internuclear distance in a single homonuclear bond

First ionisation energy of an element

The minimum energy required to completely remove the most loosely bound electron in its ground state from a mole of neutral gaseous atoms of the element

Radioactivity

The spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation.

Hlaf life of an element

The time taken for half of the nuclei in any sample of that element to decay

(Radio)carbon dating

A technique used to determine the age of an object containing carbon. It is based on the ration of carbon-14 to carbon-12 in the object

Mole

the amount of a substance that contains as many particles as there are atoms of carbon-12 in 12 grams of carbon-12

Gas

A substances that has no well-defined boundaries but diffuses rapidly to fill any container in which it is placed

Boyle's Law

At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.

Charles' law

At constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature measured on the Kelvin scale.

Gay-Lussac's law of combining volumes

In a reaction between gases, the volumes of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers, provided the volumes are measured at the same temperature and pressure.

Avogadro's law

Equal volumes of gases contain equal numbers of molecules under the same conditions of temperature and pressure

Assumptions of the kinetic theory of gases

1. Gases are made up of particles in continuous rapid, random motion, colliding with each other and with the walls of their container

2. Τhere are no attractive or repulsive forces between the molecules

3. The volumes of the molucules are negligible compared to the distances between them

4. All collisions between molecules are perfectly elastic

5. The average kinetic energy of the molecules is directly proportional to the temperature, measured on the kelvin scale

Ideal gas

one that perfectly obeys all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure

Real gases differ from ideal gases because...

1. Forces of attraction and repulsion do exist between the molecules

2. The volumes of the molecules are not negligible

Acid (Arrhenius)

A substance that dissociates in water to produce H+ ions

Strong acid (Arrhenius)

A substance that almost completely dissociates in water to give hydrogen ions

Weak Acid (Arrhenius)

A substance that only slightly dissociates in water to give hydrogen ions

Base (Arrhenius)

a substance that dissociates in water to produce OH- ions

Srong base (Arrhenius)

A substance that almost completely dissociates in water to give OH- ions

Weak base (Arrhenius)

A substance that only slightly dissociates in water to give OH- ions

Acid (Brønsted-Lowry)

A proton donor

Base (Brønsted-Lowry)

A proton acceptor

Strong acid (Brønsted-Lowry)

A good proton donor

Weak acid (Brønsted-Lowry)

A poor proton donor

Strong base (Brønsted-Lowry)

A good proton acceptor

Weak base (Brønsted-Lowry)

A poor proton acceptor

Conjugate acid-base pair

A pair consisting of an acid and a base that differ by one proton

Neutralisation

The reaction between an acid and a base to form a slat and water

Standard Solution

a solution whose concentration is accurately known

Primary standard

A substance that can be obtained in a stable, pure and soluble solid form so that it can be weighed out and dissolved in water to give a solution of accurately known concentration

Titration

A laboratory procedure where a measured volume of one solution is added to a known volume of another solution until the reaction is complete.

Oxidation (in terms of electron transfer)

loss of electrons

Reduction (in terms of electron transfer)

gain of electrons

Oxidising agent

A substance that brings about oxidation in other substances

Reducing agent

A substance that brings about reduction in other substances

Oxidation number

the charge that an atom has or appears to have when electrons are distributed according to certain rules

Rules for assigning oxidation numbers:

1. The oxidation number of an uncombined atom is 0

2. The oxidation number of an ion is equal to its charge

3. The sum of the oxidation numbers in a neutral compound is 0

4. Oxygen atoms have an oxidation number of -2, except in peroxides and OF2

5. Hydrogen has an oxidation number of -1, except in metal hydrides

6. The halogens have an oxidation number of -1 in compounds, unless bonded to a more electronegative element

Oxidation (in terms of oxidation number)

An increase in oxidation number

Reduction (in terms of oxidation number)

A decrease in oxidation number

Rate of reaction

The change in concentration per unit time of any one reactant or product

Factors affecting rate of reaction

1. Nature of reactants

2. Particle size

3. Concentration

4. Temperature

5. Catalysts

Catalyst

A substance that alters the rate of a chemical reaction but is not consumed in the reaction

Enzyme

A substance produced by a living cell that acts as a biological catalyst

Homogenous catalysis

Catalysis in which both the reactants and the catalyst are in the same phase

Hetrogenous catalysis

Catalysis in which the reactants and the catalyst are in different phases

Autocatalysis

Catalysis in which one of the products of the reaction acts as a catalyst for the reaction

Catalytic converter

A device in the exhaust system of a motor vehicle which contains catalysts to convert pollutants in the exhaust gases to less harmful substances

Catalysts in catalytic converters:

Platinum, palladium, rhodium

Catalyst poison

A substance that makes a catalyst inactive

Effective collision

One that results. in the formation of products

Activation Energy

The minimum energy that colliding particles must have for a reaction to occur, i.e. the minimum energy required for effective collisions betweeen particles to occur

Reaction Profile Diagram

A graph which shows the change in energy of a chemical reaction with time as the reaction progresses

Reversible reaction

one in which the products react to give back the reactants, i.e. the reaction is going in both directions

Chemical equilibrium

A state of dynamic balance in a reversible reaction in which the rate of the forward reaction is the same as the rate of the backward reaction

Le Chatelier's Principle

If a stress is applied to a system at equilibrium, the system re-adjusts to relieve the stress applied

Temperature, pressure and catalyst used in the Haber Process:

500°C, 200 atmospheres, iron

Temperature, pressure and catalyst used in the contact process

450°C, (just above) 1 atmosphere, vanadium pentoxide

pH

The negative logarithm to the base ten of the hydrogen ion concentration measured in moles per litre

Acid-base indicator

A substance that changes colour according to the pH of the solution in which it is placed

Range of an indicator

The pH interval over which there is a clear change of colour for that indicator

Range of methyl orange

3.1 - 4.4

Range of phenolphthalein

8.3 - 10

Hard water

Water that will not easily form a lather with soap. Caused by dissolved Mg 2+ or Ca 2+ ions

Temporary hardness

Harness that can be removed by boiling the water

Permanent Hardness

Hardness which cannot be removed by boiling the water

EDTA stands for...

ethylenediamenetetraacetic acid

Buffer solution

A solution that resists changes in pH, i.e. it keeps the pH constant

Stages in water treatment:

screening, flocculation, sedimentation, filtration, chlorination, fluoridation, pH adjustment

Flocculation

The coming together (coagulating) of small suspended particles in water

Biochemical oxygen demand

The amount of dissolved oxygen consumed by biological (biochemical) action when a sample of water is kept at 20°C, in the dark, for five days